An abrasive composition with an electrolytic water and a polishing process with the use of said abrasive composition

Abstract: An abrasive composition comprising abrasive grains of an inorganic material dispersed in a dispersion medium, characterized in that said dispersion medium contains an electrolytic water. A process for polishing an object using said abrasive composition. The abrasive composition enables to attain a high quality polish-finished surface at an improved polishing efficiency.

Description: The present invention relates to an improved abrasive composition and a process for polishing an object (a material to be treated) with the use of said abrasive composition. More particularly, the present invention relates to an improved abrasive composition which enables to attain a precisely polished surface for an object at an improved processing efficiency and a process for polishing an object with the use of said abrasive composition at an improved processing efficiency wherein a precisely polished surface is afforded for said object. There are known a number of abrasive processing methods for polishing the surface of an object (a material to be treated) using an abrasive composition comprising abrasive grains dispersed in a dispersion medium. Specifically, those abrasive finishing methods include abrasive finishing method, lapping method, blast finishing method (including sandblasting, shot peening, and liquid-honing methods), buffing method, and barrel finishing method. These surface processing methods are selectively employed depending upon the kind, hardness, or surface roughness of an object to be treated or other processing conditions involved. In recent years, there is an increased demand for attaining a polished surface with a high precision not only for optical lenses but also for other glass members such as glass substrates used in optical discs, active matrix type liquid crystal displays, and color filters for liquid crystal televisions, glass substrates for liquid crystal displays used in watches, electronic calculators, and cameras, glass substrates used in solar cell modules, and glass substrates used in LSI photomasks. Further, in recent years, in the surface-processing of wafers including single crystal silicon wafers and compound semiconductor substrates which are frequently used as support members in integrated circuits, magnetic memory hard discs, and laser members, the requirement for the flatness of a processed-surface and the requirement for the presence of defects (including scratch, orange peel, pits, nodules, and crack) at a processed-surface have been remarkably advanced. In addition to these factors, there is an increased demand for reducing the production cost by attaining an improvement in the productivity while reducing the quantity of defective products. Now, for instance, in the case of polishing the surface of a glass member such as optical lens, glass substrate, or the like, there can be mentioned an abrasive composition as one of the processing conditions. The abrasive composition in this case basically comprises abrasive grains dispersed in a liquid medium as a dispersion medium. The abrasive grains are usually of cerium oxide, zirconium oxide or silicon dioxide. The liquid medium usually comprises water. As the water herein, there is usually used treated water obtained by subjecting ground water or tap water to ion-exchange treatment or filtration treatment. And the abrasive composition usually comprises a slurry comprising grains of one of the above mentioned inorganic compounds dispersed in the above mentioned treated water as the liquid medium. However, any conventional surface processing method is accompanied by disadvantages in terms of the surface processing efficiency, specifically such that the productivity is poor in realization of a precisely polished state at the surface of an object, particularly in the case where the object comprises a material with a high hardness, and the rate of doing work per unit power is relatively small. Under such circumstances as above described, there is an increased demand for attaining an improvement not only in the abrasive composition used but also in the processing precision and in the processing speed (or the polishing speed). The present invention is aimed at eliminating the foregoing problems in the conventional polishing methods, complying with the foregoing demands, and providing an improved abrasive composition which enables to attain a precisely polish-finished surface for a material to be treated at an improved processing efficiency. Embodiments of the present invention provide an improved abrasive composition comprising grains of an abrasive dispersed in a dispersion medium comprising a specific electrolytic solution, which enables to polish a material to be treated so as to have a precisely polish-finished surface at an improved polishing speed and at an improved polish-processing efficiency. Furthermore, embodiments of the present invention provide an improved abrasive composition comprising grains of an abrasive dispersed in a dispersion medium comprising a specific electrolytic solution, which enables to attain a precisely polish-finished surface for a material to be treated for a short period of time. Also, embodiments of the present invention provide an improved abrasive composition comprising grains of an abrasive dispersed in a dispersion medium comprising a specific electrolytic solution, which enables to attain a precisely polish-finished surface for a material to be treated with the use of the abrasive in a relatively small amount wherein an abrasive pad is only slightly worn or deteriorated. According to the present invention there is provided an abrasive composition suitable for polishing an object, comprising abrasive grains of an inorganic material dispersed in a dispersion medium, wherein said dispersion medium comprises an aqueous medium containing an anode water obtained by subjecting water to electrolysis. There is also a provided a process for polishing a material to be treated with the use of the above described abrasive composition. In particular, the aforesaid abrasive composition is used in a polishing process of contacting a surface of an object to be polished with an abrasive composition suitable for polishing said object, and applying a relative motion between the surface of the object and the abrasive composition. It is acknowledged that it has been known to use a cathode water in a polishing process. In Soviet Patent SU-A-1712393 there is described a process of polishing objects of metals, non-tungsten hard alloys, and ceramics materials using an abrasive disk of diamond abrasive grains and a binder. This disk is lubricated and cooled by means of a lubricating-cooling liquid comprising cathode water, pure water, and dissolved salts of sodium nitrite, bi-substituted sodium phosphate, and iron ammonium sulphate. In the accompanying drawings: FIG.1 is a schematic diagram illustrating an apparatus for producing an electrolytic water used in the present invention. The present inventors have made extensive studies in order to eliminate the foregoing problems in the conventional polishing technique while complying with the foregoing demands and in order to attain the object of the present invention. As a result, they have found that when a specific electrolytic water is incorporated into an abrasive composition, the abrasive composition enables to eliminate the problems in the conventional polishing technique and comply with the demands and it enables to attain a defect-free polish-finished surface excelling in quality for a material to be treated at an improved polish-finishing efficiency and at a markedly improved process speed without damaging the material. The present invention has been accomplished based on this finding. The present invention provides an improved abrasive composition comprising an abrasive dispersed in an aqueous dispersion medium containing an anode water. The aforementioned abrasive composition is usable in any of the conventional surface-finishing methods wherein the abrasive composition enables to attain a precisely polish-finished defect-free surface for a material to be treated at an improved polishing efficiency and at a markedly improved process speed. The present invention includes a process for polishing the surface of a material to be treated with the aforesaid abrasive composition. The process according to the present invention enables to attain polish-finishing of a material to be treated with the use of the abrasive in a relatively small amount at an improved polishing efficiency and at a markedly improved process speed wherein a precisely polish-finished defect-free surface is effectively provided for the material without damaging the material and wherein an abrasive pad is only slightly worn or deteriorated. The anode water used in the present invention is an electrolytic water (the anolyte) obtained by subjecting given water to electrolytic treatment using an appropriate apparatus for producing an electrolytic water (this apparatus will be hereinafter referred to as electrolytic treatment apparatus), for example, of the constitution shown in FIG. 1. In FIG. 1, reference numeral 1 indicates the entire of an electrolytic treatment apparatus, reference numeral 2 a diaphragm, reference numeral 3 an anode, reference numeral 4 a cathode, reference numeral 5 a water-supply port, reference numeral 6 a take-up port for anolyte (i.e. anode water), and reference numeral 7 a take-up port for catholyte. In the electrolytic treatment apparatus shown in FIG. 1, starting water is supplied into the electrolytic treatment apparatus 1 through the water-supply port 5, and a DC voltage is applied between the anode 3 and the cathode 4 wherein cation-containing water (hereinafter referred to as cathode water or catholyte) is gathered on the cathode 4 side and anion-containing water (hereinafter referred to as anode water or anolyte) is gathered on the anode 3 side. The catholyte is taken out through the take-up port 7, and the anolyte is taken out through the take-up port 6, wherein the catholyte is of an acidic property and the anolyte is of an alkaline property. According to the electrolytic treatment apparatus, there can be obtained an electrolytic water of a given pH value of 3 to 11 by properly adjusting the DC voltage applied between the anode and the cathode or the amount of the water taken out through either the take-up port 6 or the take-up port 7. Alternatively, an electrolytic water of a desired pH value can be obtained by properly selecting the position of the port through which either the anolyte or the catholyte is taken out. Other than the electrolytic treatment apparatus shown in FIG. 1, there can be used an electrolytic water-producing apparatus described in Japanese Unexamined Patent Publication No. 11693/1989, No. 38293/1991, or No. 238084/1991 for obtaining the anode water used in the present invention. The starting water used in the above may be ground water or tap water. Alternatively, it may be ion-exchanged water. The anode water used as the dispersion medium in the present invention may be the above anolyte. Alternatively, it may be electrolytic water obtained by subjecting the anolyte to filtration treatment or ion exchange treatment. The use of such electrolytic water having a desired pH value as the dispersion medium results in obtaining a desirable abrasive composition with a desired pH value without using any additive. The aforesaid abrasive composition may be properly adjusted to have a desired pH value which is compatible with the constituent of a material to be treated. Particularly, in the case where the material to be treated is a glass member which is liable to be corroded during the polishing operation due to the acidic or alkaline property of an abrasive composition used, the abrasive composition according to the present invention may be properly adjusted to have an appropriate pH value so that such glass member is not suffered from corrosion due to the abrasive composition. Further, the pH value of the abrasive composition according to the present invention may be properly adjusted so that aggregation of the abrasive is not occurred in the abrasive composition even in the case where it is stored over a long period of time. The aforesaid abrasive composition is further advantageous in that it is free of secondary effect-like problems including corrosion or wear of a polishing apparatus, and negative influences to a material to be treated and that it is not harmful to the human body and it does not cause a drainage problem. As above described, the electrolytic water used in the present invention is the anolyte (that is, the anode water). The anode water comprises a cluster rich in anion. In the case of using abrasive grains having a property to bear negative charges around their periphery, it is desired to use the anode water rich in anion as the dispersion medium. In this case, there is afforded a desirable abrasive composition in which the abrasive grains are uniformly dispersed in the anode water as the dispersion medium without the abrasive grains being aggregated, in spite of using no dispersing agent. The reason for this is considered that the negative charges of the abrasive grains and the anions of the anode water are mutually reacted to cause an electric repulsive force which enhances the abrasive grains to be dispersed in the anode water in a state that the abrasive grains are not aggregated. A high quality abrasive composition in which abrasive grains are desirably dispersed without being aggregated is attained by using a specific electrolytic water comprising the foregoing anode water as a dispersion medium without using any additional dispersing agent. The anode water as the dispersion medium for the abrasive grains provides a surface activity. Because of this, when the abrasive composition is dedicated for polishing the surface of a material to be treated, the abrasive composition readily enters into the surface fine structure of the material whereby a excellently polish-finished surface is attained for the material at an improved polishing efficiency. Now, electrolytic water has a smaller cluster size than ordinary water, such as ground water or tap water. Particularly, ordinary water comprises a so-called compound of 18 in molecular weight and composed of one oxygen atom and two hydrogen atoms and it takes not such a structure in which water molecules are individually present but a so-called cluster structure comprising an aggregate of water molecules, because hydrogen bonds among the water molecules are strong. Incidentally, in the reports at the 1991 March conference of the Japan Chemical Society, there are described that a mass of water molecules and the magnitude of a water cluster can be measured by NMR (nuclear magnetic resonance) and that the measured results of 17 O-NMR/water at a line width (20 °C) revealed 119 Hz for rainwater, 105 Hz for well water, 118 Hz for distilled water, and 59 Hz for electrolytic water (cathode water) wherein the smaller the measured value is, the smaller the water molecule mass or the water cluster is. Based on the results measured by NMR (nuclear magnetic resonance), the magnitude of the cluster of electrolytic water was found to be 1/2 or less over that of ordinary water (ground water or tap water). It is considered that this situation wherein the electrolytic water has a small cluster size contributes to dispersing the abrasive grains in the electrolytic water without the abrasive grains being aggregated, resulting in providing a high quality abrasive composition which can be maintained in a stable state with no occurrence of aggregation of the abrasive grains even when stored over a long period of time. And as above described, when the abrasive composition is dedicated for polishing the surface of a material to be treated, the abrasive composition readily enters into the surface fine structure of the material whereby an excellently polish-finished surface is attained for the material at an improved polishing efficiency. Further, in an abrasive composition which is obtained by using a specific electrolytic water comprising the anode water comprised of a cluster rich in anion as the dispersion medium, the anions of the electrolytic water repel each other because of their electric repulsive force and the cluster of the electrolytic water is of relatively small size. Because of this, when it is dedicated for polishing the surface of a material to be treated, there is provided a pronounced effect in that the dispersion medium comprising the electrolytic water is readily vaporized to effectively release heat generated upon polishing the surface of the material with the abrasive grains, whereby an excellently polish-finished surface is attained for the material at an improved polishing efficiency. The aforesaid abrasive composition is advantageous in that it is free from secondary effect-like problems including corrosion or wear of a polishing apparatus and negative influences to a material to be treated and that it is not harmful to the human body and it does not cause such drainage problems found in the case of conventional abrasive compositions. Now, as the abrasive grains used in the aforesaid abrasive composition there can be selectively used grains (or particles) of an appropriate inorganic material as long as they have a property of providing mechanical effects to the surface of a material to be treated upon polishing treatment. Specific examples of such inorganic material are natural inorganic materials such as natural diamond, corundum, spinel emery, garnet, and silica stone; and synthetic inorganic materials such as synthetic diamond, alundum, carborundum, boron carbide, lanthanum carbide, zirconium carbide, tungsten carbide, boron nitride, titanium nitride, zirconium nitride, titanium boride, ceric oxide, chromium oxide, and ferric oxide (Bengals). Other than these, there can be mentioned emery, silica sand, manganese steel ball, glass beads, powdery iron, and silica diatomaceous earth. These inorganic materials can be used either singly or in combination of two or more of them. In addition, there can be used barrel finishing medias. The aforesaid abrasive composition may be prepared in the same manner as in the case of preparing a conventional abrasive composition, except that the liquid dispersion medium used in the preparation of the conventional abrasive composition is replaced by the foregoing anode water. Incidentally, as the liquid dispersion medium used in the preparation of a conventional abrasive composition, there is used a fatty oil series liquid such as seed oil, olive oil, or the like or a petroleum series liquid such as light oil, machine oil, or mineral oil. In the present invention, none of these fatty oil series liquids and petroleum series liquids, used in the preparation of a conventional abrasive composition, is used. Hence, the aforesaid abrasive composition excludes a water-free abrasive composition. In the aforesaid abrasive composition, the aqueous dispersion medium in which the abrasive grains are to be dispersed is desired to consist of the foregoing anode water only. However, if necessary, the dispersion medium may contain ordinary water in a small amount. In the preferred embodiments, the abrasive composition does not contain any additive such as a dispersing agent. However, it may contain an appropriate additive as long as this does not hinder the functions of the anode water as the dispersion medium. The anode water used in the aforesaid abrasive composition is not limited only to that obtained in the foregoing manner using the electrolytic treatment apparatus. The aforesaid abrasive composition is desirably applicable in any of the conventional polishing manners in which an aqueous abrasive composition is used. In the following, the features and advantages of the present invention will be described in more detail with reference to an example, which is not intended to restrict the scope of the present invention. Example 1 and Comparative Examples 1 and 2 Example 1 As a dispersion medium, there was obtained an electrolytic water comprising an anode water of pH 3.8 by using a commercially available electrolytic water-producing apparatus (trademark name: MINESOFTMS-800, produced by Akai Electric Co., Ltd.). 500 g of powdery cerium oxide having a mean particle size of 0.3 µm was introduced into 10 lit. of the anode water to obtained a mixture. The mixture was well mixed and homogenized. Thus, there was obtained an abrasive composition (hereinafter referred to as abrasive composition A). Comparative Example 1 As a dispersion medium, there was provided distilled water. 500 g of powdery cerium oxide having a mean particle size of 0.3 µm was introduced into 10 lit. of the distilled water to obtained a mixture. The mixture was well mixed and homogenized. Thus, there was obtained a comparative abrasive composition (hereinafter referred to as abrasive composition B). Comparative Example 2 As a dispersion medium, there was provided water having a pH value of 3.8 obtained by adding hydrochloric acid (HCl) to distilled water. 500 g of powdery cerium oxide having a mean particle size of 0.3 µm was introduced into 10 lit. of said water to obtained a mixture. The mixture was well mixed and homogenized. Thus, there was obtained a comparative abrasive composition (hereinafter referred to as abrasive composition C). Evaluation As for each of the above abrasive compositions A, B and C, its polishing efficiency was evaluated in the following manner. That is, there were provided 15 optical lenses made of LaSF and having a size of 33 mm (diameter) x 10 mm (thickness). In the evaluation of the polishing efficiency as for each abrasive composition, 5 of said optical lenses were fixed on a disk of a conventional lapping apparatus wherein the five optical lenses were subjected to plane lapping treatment for 10 minutes by press-contacting an abrasive sheet made of urethane resin to the disk having the five optical lenses thereon at a polishing load of 100 g/cm 2 while rotating the disk at 80 r.p.m. and while supplying the abrasive composition at 200 ml/min. Then, as for each of the five lenses having been subjected to the plane lapping treatment, there was measured a reduction in the weight. The measured results are collectively shown in Table 1. In Table 1 there is also shown a mean value among the measured results. Based on the evaluated results obtained, it was found that the polishing efficiency of the abrasive composition A (wherein the weight reduction is 12.9 in terms of the mean value) is apparently surpassing that of the abrasive composition B (wherein the weight reduction is 9.7 in terms of the mean value) and also that of the abrasive composition C (wherein the weight reduction is 9.6 in terms of the mean value). In addition, as for each of the five lenses treated by way of the plane lapping treatment obtained in the case of using each of the abrasive compositions A, B and C, its finished surface was observed by a microscope. As a result, it was found that the quality of the finished surface obtained using the abrasive composition A is apparently better than that of the finished surface obtained using any of the abrasive compositions B and C. the reduced amount by the polishing treatment (mg) mean value abrasive composition A 12.9 12.8 13.1 12.7 12.9 12.9 abrasive composition B 9.8 9.7 9.9 9.6 9.5 9.7 abrasive composition C 9.6 9.7 9.6 9.6 9.4 9.6

Claims: An abrasive composition suitable for polishing an object, comprising abrasive grains of an inorganic material dispersed in a dispersion medium, wherein said dispersion medium comprises an aqueous medium containing an anode water obtained by subjecting water to electrolysis. An abrasive composition according to claim 1, wherein the abrasive grains have a property of bearing negative charges at their periphery, and said abrasive grains are used together with the anode water. An abrasive composition according to claim 1, wherein the abrasive grains comprise emery, silica sand, manganese steel ball, glass beads, powdery iron, or powdery silica diatomaceous earth. An abrasive composition according to claim 1, wherein the dispersion medium consists of the anode water only. A polishing process comprising: contacting a surface of an object to be polished with an abrasive composition, and applying a relative motion between the surface of the object and the abrasive composition, wherein the abrasive composition comprises abrasive grains of an inorganic material dispersed in a dispersion medium comprising an aqueous medium containing an anode water obtained by subjecting water to electrolysis. The process according to claim 5, wherein the abrasive grains have a property of bearing negative charges at their periphery, and said abrasive grains are used with the anode water. The process according to claim 5, wherein the abrasive grains comprise emery, silica sand, manganese steel ball, glass beads, powdery iron, or powdery silica diatomaceous earth. The process according to claim 5, wherein the dispersion medium consists of the anode water only.

Inventors: KOBAYASHI MASATSUME, TAKEMASA KOJI, KOBAYASHI, MASATSUME, TAKEMASA, KOJI, KOBAYASHI, MASATSUME, C/O CANON K. K., TAKEMASA, KOJI, C/O CANON K. K.
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: C09K3
IPC codes: B24C11, C09K3, B24B37